It is well known in inhalation therapy that gases which are to be delivered to a subject or patient should be humidified prior to inhalation by the subject. Exemplary of the type of gases delivered to a patient will include oxygen as well as a mixture of air and oxygen which are generally mixed by an air entrainment device or system of the type generally employing a venturi tube and causing a pressurized mixing of the gases. This invention relates to an improved humidification system for accomplishing the humidification of gases delivered to a patient which system avoids many of the problems of various of the prior art units as well as permitting the further use of a gas entrainment system upstream of the humidification system.
One of the most common humidification systems involves the use of a chamber having a quantity of water therein, the chamber having a gas inlet port and a gas outlet port. Gas is delivered to the chamber through the inlet port and is bubbled through the water in order to raise the humidity of the gas afterwards which the gas is then directed to the gas outlet for delivery to the patient. And it is also accepted practice to incorporate a heater assembly with the chamber such that the water within the chamber is maintained at elevated temperatures in order to both heat and moisten the gases as the same passes through the chamber. One of the problems associated with the use of a gas bubbling system is that the bubbling of the gas through the water causes resistance and hence, in order to effectively operate the system, the gas must usually be pressurized in order to overcome the resistance encountered by the gas when entering and bubbling through the water. Where pressurizing of the gas is necessary, the possibility of utilizing an air or gas entrainment system upstream of the humidification system is magnified for the reason that in order to utilize an entrainment system of the venturi tube type, it is necessary to minimize the resistance of gas flow of the gases passing therethrough. It is therefore apparent that if the gas is to be pressurized prior to passing the same through the humidification system, it becomes very difficult if not impossible to also employ an air or gas entrainment system upstream from the humidification system. Furthermore, it is desirable to provide a humidification system which is more efficient and units heretofore known in the art which are also simplified in construction and permit ease of use.
Various other types of systems have been proposed for humidifying gases, generally for use in connection with respiratory care systems. For example, another humidification unit presently commercially available includes a chamber suitable for containing a quantity of water and wherein the bottom wall has a heater plate associated therewith. An aluminized insert element is provided which is formed of aluminum and constructed in the form of a spiral within the chamber. Between the concentric loops of the spiral there is positioned a sheet of absorbent paper in loose fitting relationship, the absorbent paper being manually fed into the spiral until the same is present between all of the concentric loops of the spiral. The aluminum element functions to conduct heat from the lower heater plate upwardly while the absorbent paper functions to take water up by capillary action thereby to provide moisture throughout the spiral assembly. A gas is inserted into the unit and must be specifically directed to the open end of the spiral with the necessity that the gas completely pass through the open concentric circles of the spiral and exit from the innermost portion of the spiral upwardly to a gas outlet and from there into an outlet tube for delivery to a subject. This unit is manufactured by the Fisher & Paykel Limited Company in Auckland, New Zealand and is distributed by OEM Medical Inc. of Edison, N.J. However, there would appear to be several drawbacks incident to the use of such a humidification device including the fact that the absorbent material must be manually wound into the spiral member by the operator. Hence, the absorbent material is not securely fixed to or bonded or laminated to the spiral aluminum member and this feature raises certain other difficulties. For example, the operator cannot adjust the physical distance or separation between the paper absorbent material and the concentric sides of the spiral member and hence there will be a variance in the spacing of the paper from the surface of the spiral member from one position to the next. The result is that as the gas flows through the spiral unit, a significant amount of resistance is met by the gas, and as the gas flow increases through the unit, the resistance will increase significantly. As has been previously indicated, when the resistance of the gas flow rate is increased, the possibility of utilizing an air entrainment device upline from the humidification system is greatly increased since in order to overcome the increase in resistance, it is necessary to pressurize the gas as it is delivered into the humidification unit. If the gas is pressurized prior to delivery to the humidification system, it becomes increasingly difficult if not impossible to utilize a venturi type entrainment device for mixing a quantity of oxygen with air upstream from the humidification system. Another drawback incident to the New Zealand unit resides in the fact that the gas must be directed into the spiral member along the outermost open edge in order that the gas pass through and around all of the loops of the spiral and exit from the immediate center of the spiral. Hence, it is necessary to establish a specific gas flow in order for the unit to function efficiently, and lacking such an air flow, the gas will not become efficiently humidified. Finally, it is to be noted that the manual insertion of the paper absorbent material within the spiral loop is a difficult operation consuming time thereby rendering the unit difficult to use and detracting from its overall commercial desirability.
Still another humidification unit which is described in the art relates to a temperature and humidity control unit developed by NASA and described in NASA TECH BRIEF Document No. B 72-10660. The unit described in this publication shows a temperature-humidity subsystem which is formed by a chamber suitable for carrying a quantity of water therein, the chamber being divided into three sub-chambers. The first chamber is adjacent the inflow line for the gas and contains a quantity of water therein and is in fluid communication with a reservoir for maintaining the water level in the lower chamber. The central chamber is formed by a pair of opposed perforated aluminum plates fixedly secured to a heater member which is in turn afixed to the bottom of the chamber. A plurality of gauze surgical sponge pads are packed into the second chamber extending from one of the perforated plates to the opposed perforated plate. The third chamber consists of the outflow chamber and is to the downstream side of the gauze surgical sponge. In point of fact, the unit was developed as a device for simulating exhaled human breath incident to various research work engaged in by NASA, however, it is believed that the device could similarly function as a humidification system for gas passed therethrough. The significant problem associated with the subject device, however, relates to the fact that it is flow-through type system in that the gas, in order to become humidified, must be passed through the first perforated plate, the gauze surgical sponge, and then through the opposed perforated plate before it exits the unit. Generally, the problems discussed above with other prior art units are similarly involved in the unit described herein in that as gas flows through the gauze surgical sponge, a significant amount of resistance is incurred and the resistance does increase as the gas flows through the surgical sponge. As indicated previously, when resistance is encountered and is increased during the operation of the humidification system, it is necessary to pressurize the gas in order to force the same through the unit. By pressurizing gases prior to delivery to the humidification system, it then becomes difficult if not impossible to employ gas entrainment devices upstream of the humidification system and this is generally regarded as a drawback in respiratory systems utilizing such humidification devices.
Another drawback of the unit described in the NASA TECH BRIEF is the fact that the perforated plates do not appear to conduct heat throughout the center chamber and hence, the gas passing through the gauze surgical sponge is not adequately humidified at elevated temperatures so that when the gas does reach the subject, the gas will not be efficiently humidifed. Furthermore, since heat is not conducted throughout the chamber area, it is quite obviously necessary to operate at higher temperatures in order to attempt to achieve some degree of elevated temperatures within the chamber in order to heat the gas as the same is being humidified. In addition, due to the structure of the unit, assuming that the two perforated plates do conduct heat, there will be a stratification of heat temperature throughout the chambers since the gas will be heated as it passes through the first perforated plate and cooled by evaporation as it passes through the gauze surgical sponge. When the gas finally reaches the opposed perforated plate, it will be once again heated and this heating-cooling-heating cycle causes a differential of heating of the gas and while the gas may be substantially humidified, the method of achieving such humidification is less efficient and greater amounts of heat are necessary.
Another further drawback incident to the device disclosed in the NASA TECH BRIEF is the fact that a water reservoir is provided for allegedly maintaining the water level in the three chambers below a constant level. However, due to the fact that the gases must be pressurized in order to force the same through the unit, the pressure will cause a variance of the water level in the reservoir and it is conceivable that the water level could rise with a resultant loss in efficiency, or the water level could lower to a point below the absorbent gauze surgical sponge after which there would be little to no humidification occuring since the sponges would no longer be wet and due to the lack of proper heat conduction by the perforated plates, there would be little heat in the chamber to vaporize what remaining water is in the chamber and cause vapor throughout the chamber. Hence, it is quite possible that the gas would not be humidified at all if the unit should run out of water or have the water level reduced to a level below the gauze surgical sponge.
Not withstanding the specific drawbacks of specific prior art units discussed above, generally, the prior art units are cumbersome in construction and rather expensive to manufacture. Furthermore, generally these units are difficult to set up and operate and hence, the amount of setup and operating time as well as cleanup time is a significant problem.